Upper motor neurons in cerebral cortex (primary motor cortex)

1. Corticospinal and corticobulbar pathways: upper motor neurons that initiate complex voluntary movements • Functional organization of the primary motor cortex • Premotor cortex • Damage to descending motor pathways 03-55-485

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3. Corticospinal and corticobulbar pathways: upper motor neurons that initiate complex voluntary movements • Upper motor neurons in cerebral cortex (primary motor cortex) • In adjacent and interconnected areas of the frontal lobe • Together mediate planning & initiation of complex temporal sequences of voluntary movements. 03-55-485

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5. Corticospinal and corticobulbar pathways Primary motor cortex receives regulatory input: • From basal ganglia and cerebellum -> relays in ventrolateral thalamus • From sensory regions of the parietal lobe 03-55-485

6. Primary motor cortex • Low threshold for eliciting movements through electrical stimulation • Descending pathways to lower motor neurons in the brainstem and spinal cord. 03-55-485

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8. Organization of the primary motor cortex • Upper motor neurons are pyramidal cells in layer V. • Their axons descend to the brainstem and to spinal motor center in the corticobulbar and corticospinal tracts. • --> then run to the base of the pons • --> to medulla through medullary pyramids…. 03-55-485

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10. Lateral corticospinal tract • Direct pathway from the cortex to the spinal cord (lateral portions of the ventral horn and intermediate gray matter) 03-55-485

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12. Indirect pathway • from motor cortex to 2 sources of upper motor neurons in the brainstem (red nucleus and reticular formation) • Motor cortex--> reticular formation --> medial region of the spinal cord. • Motor cortex--> red nucleus--> lateral region of the spinal cord. 03-55-485

13. Functional organization of the primary motor cortex • When stimulated, muscles on the opposite side of the body contract. • Has complete representation of body’s musculature. • Greater space for fine motor control than for less precise motor control • Very focal stimulation --> organized movement (excitation and inhibition) 03-55-485

14. Motor Cortex • Overlap of regions that initiate different movements. • A particular movement can be elicited by widely separated sites. 03-55-485

15. Motor cortex • Recorded neural activity during voluntary movement. • Motor cortex neurons direct recruitment of lower motor neurons • Force • Direction 03-55-485

16. Motor cortex • Upper motor neurons encode a movement rather than individual muscles. • A movement can involve several different lower motor neuron pools • Each arm movement is encoded by concurrent discharges of a large population of neurons 03-55-485

17. Premotor cortex -movement selection • Reciprocal connections • with the primary motor cortex • And project axons through corticobulbar and corticospinal pathways • Uses information from other cortical regions • Active during association of visual (sensory) to movement. 03-55-485